Transmitter with vibratile air coupling



Sept. 23, 1958 G. A. COATES 2,853,146

TRANSMITTER WITH VIBRATILE AIR COUPLING Filed Feb. 7, 1955 viz/1111113 l I; III/1111A Fig. 4

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2,353,146 Patented Sept. 23, 1958 ice TRANSMITTER WITH VIBRATILE AIR COUPLING George A. Coates, San Diego, Calif.

Application February 7, 1955, Serial No. 486,744

11 Claims. (Cl. 181-31) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a device for transmitting and radiating vibration induced wave motion to a body of fiuid and, more particularly, to a device which provides both a shallow horn loading and an auxiliary vibrating medium for coupling an acoustic speaker to the surrounding air.

There are no known devices wherein a single element both guides the radiation of the excited waves and is, itself, driven by these waves to produce a secondary wave source. The rigid horns heretofore used merely guide the waves emanating from a single sound source such as a speaker cone or diaphragm. With such arrangements exceedingly large, costly and complex structures are required to produce faithful reproduction over a broad frequency range. Further, these structures lack presence or that quality in sound reproduction which gives the listener the illusion that the sound has no definite point of origin in the room.

The present invention comprises a pair of rigid, apertured, mutually spaced and rigidly interconnected frames and a sheet of tensioned, flexible, and resilient vibratory material or diaphragm secured at its ends to the respective peripheries of the apertures. Preferably the two apertures are of different size and configurations and a driving means is located closely adjacent the smaller of the two.

It is an object of this invention to provide means for etficiently reproducing a wide range of the audio spectrum with acoustic elements of restricted size which may be driven in diverse manners.

Another object of this invention is to provide a means for efliciently coupling the lower range of audio frequencies with the air and which will also effectively radiate higher frequencies.

A further object of this invention is to provide a coupling device which will have a substantially linear response over abroad frequency range.

Still another object is the provision of a parasitically driven auxiliary vibrating medium which acts as a horn to guide high frequency radiations and, while not mechanically connected to the source, will vibrate at multiple lower frequencies to excite an air mass over an area which is substantially greater than the primarily excited area.

Another object of this invention is to provide a speaker mounting which eliminates standing waves within the enclosure.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure l is a perspective view, with parts broken away, of one form of the invention;

Figure 2 is a section on line 2-2 of Figure 1;

Figure 3 is a view similar to Figure 1 of a second form of the invention and Figure 4 is a section on line 4-4 of Figure 3.

The present invention, as shown in the embodiment of Figures 1 and 2, comprises an enclosure 10 which may be of any desired shape, circular, oval, square, triangular, or free form, and is shown in the form of a rigid rectangular skeletal frame including rigid elements 12, 14, 16, 18, fixedly interconnected by suitable fastening means and having peripheral edges 20 which provide the mouth of the enclosure and define one aperture 21 thereof. A rigid backing element 22 fixed to the other edges of elements 1218, is provided with an opening 24 around the periphery of which are secured a plurality of symmetrically rarranged' spacing and fastening elements 26 which are fixed to a second rigid frame or speaker platform 28. Platform 28 is provided with an aperture 30 which is symmetrically arranged with respect to elements 26 and conforms in size and shape to the mouth of the cone of conventional speaker 32 which has its mounting flange 34 secured to the platform by suitable detachable fastening means such as screws or bolts, the speaker being in alignment with aperture 30. Opening 24 is of a size and shape to permit convenient insertion of the speaker therethrough and, most desirably, apertures 21 and 30 are of substantially different size and geometric configuration. For example, in one model, aperture 30 is a circle of seven inches diameter and aperture 21 is a rectangle, 21" by 30". The platform 28 is spaced from element 22 a distance of l and from edges 20 a distance of 7%". While elements 24, 26, 30 and 32 are symmetrically arranged with respect to each other, they may all be asymmetrically related to one or more of elements 12-18.

The vibratory diaphragm 36 comprises a sheet of reticulated material such as muslin which is provided with a continuous inner terminal portion or end which defines an opening slightly smaller than but of the same shape as aperture 30 and the edge of this opening (i. e., the inner end of the material) is stretched circumferentially and continuously secured by staples or the like to the periphery of aperture 30 which has previously been coated with a bonding agent such as airplane dope. The sheet 36 is then stretched and the continuous outer terminal portion or end thereof is continuously secured by staples or the like to edges 20 which have also been previously coated with the bonding agent. In securing the sheet to elements 12-18 it is necessary to follow the procedure set forth below in order to ensure a sheet surface which is tensioned but is free of wrinkles and soft spots. The sheet which has been arranged with its warp and woof parallel to elements 12, 14 respectively, is first stretched and secured to mid portions of adjacent elements such as 12 and 14 and is then progressively secured to points on these elements which are closer to the intersection of the adjacent elements, the tension being maintained at all times. This procedure is required because the fabric will stretch more along its bias than along the warp or woof. The fabric is similarlysecured to elements 16 and 18 and its outer surface (away from the speaker) is completely coated with the bonding agent which penetrates" a wide band resonator to vibrations of the speaker cone and is not mechanically coupled to the speaker which may be mounted completely independent of the diaphragm. Diaphragm 36 vibrates in response to the medium to lower frequency waves in the air which is in contact therewith and thereby acts as an auxiliary exciting source, at these frequencies, with a vibration radiating surface which is substantially greater than that of the speaker cone. It has been found that diaphragm 36 will effectively respond to a greater range of frequency variations when the difference between the dimensions of adjacent elements such as 12 and 14 is increased. Conversely the narrowest frequency response will occur when the shape of enclosure approaches a square or circle.

A modification of the present invention is shown in Figures 3 and 4. Enclosure 10', which may be of any desired shape, circular, oval, square, triangular or free form, is shown in the form of a rigid rectangular skeletal frame including rigid elements 12', 14', 16', 18, fixedly interconnected by suitable fastening means and having peripheral edges 26 which provide one mouth of the enclosure and define one aperture 21 thereof. Peripheral edges provide a second month of the enclosure and define the second aperture 41 thereof. A rigid interconnecting element 22' is securely fastened at its respective ends to elements 12' and 16 and is provided with an opening 24' to and around the periphery of which is secured platform element 28 containing aperture 30' which is symmetrically arranged with respect to aperture 24'. Aperture 30 conforms in size and shape to the mouth of the cone of conventional speaker 32' which has its mounting flange 34 secured to platform element 28 with suitable detachable fastening means such as screws or bolts, the speaker being in alignment with aperture 39'. Opening 24' is of a size and shape to permit .convenient insertion of the speaker therethrough and, most desirably, apertures 21 and 30', apertures 24 and 41 are of substantially different size and configuration. For example, in one model, aperture 30' is a circle of seven inches diameter and aperture 21' is a rectangular 21" by 30", and aperture 24 is a circle of 8%." diameter and aperture 41 is a rectangle 21" by 30". Element 22 is so mounted that it is equi-distant from elements 14 and 1S and may or may not be fastened at its ends on the centerline of elements 16 and 12. However, element 22 may be located either above or below in unequal relationship to elements 14' and 18. Elements 28 and 22 may be so arranged that concentric apertures 30 and 24' are off-center in respect to both horizontal and vertical centerlines .of the enclosure. This modification in cludes two diaphragms, 36' and 46, each similar to diaphragm 36. The development and mounting of diaphragms 36' and 46 are essentially the same as to stretching and treatment as previously described, diaphragm 46 being stretched between the inside of aperture 24 .and peripheral edges 40.

While the vibratory diaphragm or diaphragms of this invention are shown as being excited by a speaker, other sound sources may be used. The diaphragm may be incorporated in a musical instrument having as its sound source vibratory strings or reeds. It may also be used as a multiple frequency percussion instrument or drum since it will vibrate at different frequencies when different portions thereof are struck. Furthermore, the sound source, whether it be speaker or other vibratory element, need not be mounted on either of the frames to which are attached the diaphragm. The sound source may be independently mounted at a distance from the diaphragm since the latter is parasitically driven.

While there have been shown and described what are at present considered to be several preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true scope of the invention, and it is to be understood, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An audio frequency air coupling assembly comprising first rigid frame means, second rigid frame means fixedly secured to said first means and spaced therefrom, said first means having an aperture therein, said second means having an aperture therein which is smaller than said first mentioned aperture, and a sheet of flexible, resilient and tensioned material having continuous inner and outer ends, said inner end defining an opening in said sheet which is substantially coextensive with said smaller aperture, and means for continuously securing said sheet at its ends to the peripheries of respective apertures.

2. An audio frequency air coupling assembly comprising first rigid frame means, second rigid frame means fixedly secured to said first means and spaced therefrom, said first means having an aperture therein, said second means having an aperture therein which is smaller than said first mentioned aperture, an apertured sheet of flexible, resilient and tensioned material continuously secured at its inner and outer ends to the peripheries of respective apertures, and a driving means for parasitically and sympathetically exciting said material.

3. An audio frequency air coupling assembly comprising first rigid frame means, second rigid frame means fixedly secured to said first means and spaced therefrom, said first means having an aperture therein, said second means having an aperture therein which is smaller than and differs in shape from said first mentioned aperture, and an apertured sheet of flexible, resilient and tensioned material continuously secured at its inner and outer ends to the peripheries of respective apertures.

4. In a device of the class described, a pair of rigid, apertured, mutually spaced and rigidly interconnected frame means each having an aperture and an apertured continuous, tensioned, flexible and resilient vibratory means secured at the inner and outer terminal portions thereof to said frame means adjacent the peripheries of the respective apertures.

5. In a device of the class described, a first means for exciting an air mass and horn means independently fixedly mounted with respect to said first means and coupling said first means to said air mass for loading said first means and for further exciting said air mass, said horn means comprising an apertured, continuous and ten sioned vibratory diaphragm having inner and outer teriinal portions fixed in mutually spaced relation.

6. In a device of the class described, a rigid skeletal frame, an apertured speaker platform, means rigidly securing said platform to and within said frame, a speaker, means mounting said speaker on said platform in alignment with said aperture and continuous, tensioned, fiexible and resilient vibratory means secured to said platform adjacent the periphery of the aperture thereof and secured to said frame.

7. The device of claim 6, said frame being rectangular and having a first peripheral edge forming the mouth of the device, said platform securing means comprising a rigid backing element fixed to said frame at a second peripheral edge thereof and combined spacing and fastening means secured to and between said platform and backing element, said backing element having an opening receiving a projecting portion of said speaker, said platform aperture conforming in size and shape to the mouth of said speaker and said vibratory means being continuously secured to the frame at said first peripheral edge and to the platform at the walls of said aperture.

8. The device of claim 6, said frame having a pair of mutually spaced, oppositely facing peripheral edges forming a pair of mouths for the device, said vibratory means comprising a first portion secured to and between one of said peripheral edges and the periphery of said aperture and a second portion secured to and between the other 5 of said peripheral edges and the periphery of said aperture.

9. A method for constructing a device of the class described comprising the steps of forming a pair of rigid apertured frames, fixing said frames to each other in mutually spaced relation, forming a sheet of resilient, flexible material with an opening adjacent a central portion thereof which conforms in size and shape to one aperture in one of said frames, continuously securing said material at the periphery of the opening therein to the periphery of said one aperture, applying tension to said material, continuously securing said material to the periphery of one aperture in the'other of said frames, and treating said material to shrink and seal it.

10. A method for producing a vibratory membrane comprising the steps of forming an aperture in a sheet of fabric to provide an inner terminal fabric portion, an-

I choring said portion in a first endless configuration to provide a rigid walled aperture through said membrane, applying tension to said fabric, anchoring a second portion of the tensioned fabric in a second endless configuration which differs from said first configuration and treating said fabric to shrink and seal it.

6 11. A method for constructing a device of the class described comprising the steps of forming a pair of rigid apertured frames, fixing said frames to each other in mutually spaced relation, forming a sheet of resilient,

References Cited in the file of this patent UNITED STATES PATENTS 921,465 Rose May 11, 1909 1,477,553 Grissinger Dec. 18, 1923 1,672,796 Whitmore June 5, 1928 1,934,932 Lindenberg Nov. 14, 1933 2,171,940 Macnabb Sept. 5, 1939 2,224,931 Rubinstein Dec. 17, 1940 2,765,043 Muller Oct. 2, 1956 

